Thawing permafrost releases methane, a powerful greenhouse gas, but this has not yet been included in models of the future climate. Permafrost covers nearly a quarter of the northern hemisphere at present and is estimated to contain 1,700 gigatonnes of carbon – twice the amount currently in the atmosphere. As it thaws, it could push global warming past one of the key "tipping points" that scientists believe could lead to runaway climate change.

And how does the modeling upon which the predictions of a methane cataclysm, and our eventual doom, is based compare with observations of reality thus far?